Recently upgrade my PC with new CPU, Mainboard and Video card. After that Ubuntu won't start up. It says this:
PNPBIOS fault: attempting recovery
PNPBIOS: Warning! Your pnp BIOS caused fatal error. Attempting to continue
PNPBIOS: You may need to reboot with the "nobiospnp" option to operate stably
PNPBIOS: Check with your vendor for an updated BIOS
PNPBIOS: Get_dev_node: unexpected status 0x28
Starting Ubuntu...
Pivot_root: no such file or directory
/sbin/init: 429: Cannot open dev/console: no such file
Kernel panic: Attempting to kill init!

Is there any easy way to make linux work again without formatting hdd?

I think its the time to make a fresh installation. As most of the hardware is changed.

mmmh ok. If we talk about fresh installation - i guess i can reinstall linux without losing any important data? Formatting just some partitions, leaving windows partition and some folders from /home is possible?

Backup your home directory/directories, and possibly you'll be fine. You'll need to do some configuration though.
Another way that comes into my mind is a kernel reconfiguration/recompilation. Once you have a kernel for your new hardware, it wouldn't be that hard. In case you can't compile your own kernel, you'd better reinstall the OS.

You could try going into your BIOS and turning OFF "PnP BIOS"
Then try again.
HTH

Your hard drives and what is on them are not affected: the problem is that your kernel configuration no longer matches your hardware.

A good first step would be to boot from a LiveCD, then use various commands to observe how that Linux perceives your hardware. Observe (with lsmod) what kernel driver-modules were loaded. Some LiveCDs even include a hardware detection utility.

If you installed your system from a distro, try re-executing the installation process (or some of it) from the previous CD that you used. This will re-run the hardware detection procedures used by that distro.

Well the second part of this nightmare is solved: had to switch hdd's on ATA cable so they are now in position as they were on old board - as a hda2 (before restoring old positions it was as a hdc2). Now just interested in the first part of error (until Starting Ubuntu...). Basically it doesn't bother me - only after booting up linux, when should start up gnome, monitor starts to show picture as on old 8bit gaming consoles you would pull out kartridge in the middle of the game with the "kill -9" option.